The present invention relates to input devices for computer systems. In particular, the present invention relates to multi-switch input devices.
In computer systems, hand-held input devices such as mice and trackballs, are provided to allow the user to control different functions of the computer system. Most of these input devices include at least one button, which activates a switch inside the input device. The button allows the user to select items on the screen and allows the user to perform drag-and-drop functions.
To detect the closure of a switch, input devices typically include an Application Specific Integrated Circuit (ASIC) that has one input for every switch on the device. When conventional microprocessors are used for this task, an individual I/O port pin is allocated for each switch input. Thus, in a two-button mouse the detection circuit has at least two inputs and for a three-button mouse the detection circuit has at least three inputs.
To take advantage of economies of scale, some detection circuits have been designed to be used in input devices that are of the same general type but that have different numbers of switches. For example, the same detection circuit may be used in a two-button mouse and in a three-button mouse. To achieve this flexibility, these detection circuits must have as many inputs as the maximum number of switches that will be connected to the detection circuit. Thus, if a detection circuit is designed to be used in three-button mice and two-button mice it must have at least three inputs.
To reduce costs, detection circuits typically do not include excess inputs. Thus, if the maximum number of switches that will be connected to the detection circuit is three, the detection circuit typically will not have four inputs. Unfortunately, as the number of buttons on an input device increases, this strategy means that the detection circuit must be redesigned to include additional inputs. This involves costly redesign time and does not take advantage of the economies of scale available with current detection circuits.